Create About Dialog. Fixes T801

Summary:
  - Use `DialogFragment` to implement an about dialog.
  - Add transition animations when dialog launches and closes.
  - When dialog launch, show app name and version number

Test Plan:
  - Build and launch app.
  - Tap on the overflow menu to see the about menu item.
  - Tap on the about menu item.
  - See a dialog slide from the top.
  - Close the dialog.
  - See the dialog fade out.

Reviewers: dkobia

Subscribers: rjmackay

Maniphest Tasks: T801

Differential Revision: https://phabricator.ushahidi.com/D359